JP2001-200810A discusses a single-acting hydraulic cylinder including a piston rod inserted into a cylinder tube having a bottomed cylindrical shape, a piston provided in a tip of the piston rod to partition an inside of the cylinder tube into a rod-side chamber and a bottom-side chamber, and a cylinder head provided in an opening of the cylinder tube to slidably support the piston rod. In the single-acting hydraulic cylinder discussed in JP2001-200810A, the rod-side chamber is an air chamber.